1. Field of the Invention
The present invention relates to a signal correction device of photoelectric conversion equipment.
2. Related Background Art
Photoelectric conversion devices such as a CCD image sensor have been used for detection of camera focus, but with this type of charge storage sensor a dark current component generated irrespective of the injected light constitutes a factor which restricts the focus detecting performance of the sensor, particularly when brightness is low.
When brightness is low, storage time of the sensor is made longer to obtain some signal component, but the dark current component is generated in proportion to the storage time, and as a result the signal-to-noise ratio (S/N) becomes lower. In view of this problem, proposals have been made regarding compensation of the dark current component.
For example, it has been proposed to shade a section of the photoelectric conversion devices and to utilize the difference between the output of an open section and the output of the shaded section. However, this is not sufficiently effective, because it does not compensate the actual dark current component in each light receiving bit.
Japanese Patent Appln. Laid-Open No. 63-263881 discloses a compensation device wherein each light receiving bit is compensated by means of temperature detecting means and storage time counting means. The value for correction is obtained from the output of the temperature detecting means and the output of the storage time counting means in reference to the output at dark time registered in an EEPROM beforehand (dark time output being influenced by environmental temperature and storage time). Although this device has the advantage of enabling correction of each bit, it requires a separate temperature detecting means and storage time counting means, so the device is more complicated.